People took shelter wherever they could as a massive tornado descended on their Oklahoma communities Monday afternoon.

They had to move fast. First warnings came just 16 minutes before the tornado developed, according to the National Weather Service in Norman, Okla.

As TV and radio broadcasters, weather watchers and others urged residents to take shelter immediately, many took to whatever refuge they could quickly find.

A resident of Moore, Okla., said she got into her bathtub with her dog and piled on pillows for shelter.

"I just cannot believe that we actually survived this thing," she told a KFOR-TV reporter.

Another Moore resident told a KWTV reporter that she and her two children also took shelter in a bathtub -- and pulled a mattress on top of them for extra protection.

"Our whole house is gone," the distraught woman said as she held her two kids' hands. "Everything but where we were is gone."

Lando Hite, who works at a horse stable in Moore, told KFOR that he sought safety in a horse stall.

"I didn't have very long at all" before the tornado hit, he said.

While in the stall, "it was just unbearably loud," he said. "You could see stuff flying everywhere."

Others at work also had to quickly seek shelter. In advance of the storm, the Oklahoma House of Representatives stopped work so Capitol employees could seek safety in the basement.

The devastating tornado, which had winds up to 200 mph, killed at least 51 people. The terror latest 40 minutes Monday afternoon as the twister destroyed homes, cars and businesses across southern Oklahoma City and its suburbs.

At 2:45 p.m. Monday, the National Weather Service in Norman tweeted "you DO NOT want to be in your car in a tornado! Stay where you are. Get in, get down and cover up."

At 3:02 p.m., it tweeted this warning: "LARGE VIOLENT TORNADO moving toward Moore and SW OKC. Take cover right NOW!!! Do not wait!!"

On its webpage, the Oklahoma City Police Emergency Management Office warns that "when a tornado is coming, you have a short amount of time to make life or death decisions. Advance planning and quick response are the keys to surviving."

The webpage tells people at home to head to a the basement, storm cellar or the lowest level of the building. If there is no basement, it advises residents to get away from windows and to go to an inner hallway or a small inner room without windows, such as a bathroom or closet.

If someone is outdoors and no shelter is available, it advises to lie in a ditch or low-lying area or crouch near a strong building.

"Never try to outdrive a tornado," the site says. "Tornadoes can change direction quickly and can lift up a car or truck and toss it through the air."